From 182a06ffbe32479ac49e8dc35c74a3607a0f61a2 Mon Sep 17 00:00:00 2001
From: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Date: Thu, 10 Sep 2026 15:27:50 +0200
Subject: [PATCH] deb: add -j/--jobs to control parallel build jobs

By default the number of parallel jobs is detected with nproc inside
the build context. Add a -j/--jobs option so an explicit count can be
honored instead, threading it through build_binary_package and
local::build into DEB_BUILD_OPTIONS=parallel=N.
---
 src/deb/local.rs | 35 ++++++++++++++++++++---------------
 src/deb/mod.rs   |  5 +++++
 src/main.rs      | 10 ++++++++++
 3 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/src/deb/local.rs b/src/deb/local.rs
index 93b6e15..8d24412 100644
--- a/src/deb/local.rs
+++ b/src/deb/local.rs
@@ -37,6 +37,7 @@ pub async fn build(
     inject_packages: Option<&[&str]>,
     ctx: Arc<Context>,
     ui: Option<Arc<DebUi>>,
+    jobs: Option<usize>,
 ) -> Result<(), Box<dyn Error>> {
     let sink: Option<Arc<dyn LineSink>> = ui.as_ref().map(|u| u.sink());
 
@@ -45,21 +46,25 @@ pub async fn build(
     env.insert("LANG".to_string(), "C".to_string());
     env.insert("DEBIAN_FRONTEND".to_string(), "noninteractive".to_string());
 
-    // Parallel building: find local number of cores, and use that
-    let num_cores = ctx
-        .command("nproc")
-        .output()
-        .map(|output| {
-            if output.status.success() {
-                String::from_utf8_lossy(&output.stdout)
-                    .trim()
-                    .parse::<usize>()
-                    .unwrap_or(1)
-            } else {
-                1 // Default to 1 if nproc fails
-            }
-        })
-        .unwrap_or(1); // Default to 1 if we can't execute the command
+    // Parallel building: honor an explicit -j/--jobs count, otherwise detect
+    // the number of cores available inside the build context (nproc).
+    let num_cores = match jobs {
+        Some(j) => j,
+        None => ctx
+            .command("nproc")
+            .output()
+            .map(|output| {
+                if output.status.success() {
+                    String::from_utf8_lossy(&output.stdout)
+                        .trim()
+                        .parse::<usize>()
+                        .unwrap_or(1)
+                } else {
+                    1 // Default to 1 if nproc fails
+                }
+            })
+            .unwrap_or(1), // Default to 1 if we can't execute the command
+    };
 
     // Build options: parallel, disable tests by default
     env.insert(
diff --git a/src/deb/mod.rs b/src/deb/mod.rs
index 6f97cb1..658d7bf 100644
--- a/src/deb/mod.rs
+++ b/src/deb/mod.rs
@@ -33,6 +33,7 @@ pub async fn build_binary_package(
     inject_packages: Option<&[&str]>,
     ctx: Option<Arc<Context>>,
     ui: Option<Arc<DebUi>>,
+    jobs: Option<usize>,
 ) -> Result<Vec<PathBuf>, Box<dyn Error>> {
     let result = build_binary_package_impl(
         arch,
@@ -45,6 +46,7 @@ pub async fn build_binary_package(
         inject_packages,
         ctx,
         &ui,
+        jobs,
     )
     .await;
 
@@ -68,6 +70,7 @@ async fn build_binary_package_impl(
     inject_packages: Option<&[&str]>,
     ctx: Option<Arc<Context>>,
     ui: &Option<Arc<DebUi>>,
+    jobs: Option<usize>,
 ) -> Result<Vec<PathBuf>, Box<dyn Error>> {
     let cwd = cwd.unwrap_or_else(|| Path::new("."));
 
@@ -160,6 +163,7 @@ async fn build_binary_package_impl(
                     inject_packages,
                     build_ctx.clone(),
                     ui.clone(),
+                    jobs,
                 )
                 .await?
             }
@@ -414,6 +418,7 @@ mod tests {
             None,
             Some(ctx),
             None,
+            None,
         )
         .await
         .expect("Cannot build binary package (deb)");
diff --git a/src/main.rs b/src/main.rs
index 8c8b682..54dab34 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -78,6 +78,7 @@ fn main() {
                     .long_help("Cross-compile for target architecture (instead of using qemu-binfmt)\nNote that most packages cannot be cross-compiled").required(false))
                 .arg(arg!(--mode <mode> "Change build mode [local]").required(false)
                     .long_help("Change build mode [local]\nDefault will chose depending on other parameters, don't provide if unsure"))
+                .arg(arg!(-j --jobs <jobs> "Number of parallel build jobs (default: number of CPUs available in the build context)").required(false))
                 .arg(arg!(--verbose "Show raw tool output instead of the live build view").required(false)
                     .long_help("Show raw tool output instead of the live build view.\nAlso implied by RUST_LOG=debug for pkh's own logs.")),
         )
@@ -313,6 +314,14 @@ fn main() {
                 .copied()
                 .unwrap_or(false);
 
+            let jobs = sub_matches.get_one::<String>("jobs").map(|s| s.as_str());
+            let jobs = jobs.map(|j| {
+                j.parse::<usize>().unwrap_or_else(|_| {
+                    error!("Invalid --jobs value '{}': expected a positive integer", j);
+                    std::process::exit(1);
+                })
+            });
+
             // Live build view: disabled by --verbose or when stdout is not a
             // terminal (DebUi handles the non-TTY case itself)
             let ui = if verbose {
@@ -333,6 +342,7 @@ fn main() {
                     inject_packages,
                     None,
                     ui.clone(),
+                    jobs,
                 )
                 .await
             });